This invention relates to an exhaust system for an outboard motor and more particularly to an improved exhaust system that insures against the ingestion of water into the engine chambers under any running conditions.
It is well known in connection with outboard motors to employ a so-called "under the water" exhaust gas discharge for silencing the exhaust gases under high speed running. Where the engine employs multiple cylinders, it has been the practice to employ more than one exhaust pipe and the individual exhaust pipes all communicate with each other at a position that is above the water under normal high speed running. As is well known, however, the degree of submersion of the outboard motor depends upon the speed at which the associated watercraft is traveling. When traveling at low speeds or when idling, the motor is submerged normally to such a point that the common communication between the individual exhaust is beneath the water level. Under this running condition, it is the normal practice to provide an above the water exhaust so as to prevent undue back pressure on the engines. However, with many types of engines, there are conditions under which the exhaust pipe is actually at less than atmospheric pressure. This is particularly true with respect to two cycle engines due to the overlap in the exhaust and intake timing. When the exhaust passage is at a pressure that is less than atmospheric and when the water level in the exhaust pipe is high, there exists a possibility that water may be drawn back into the engine chambers under this condition. This can in some instances cause problems for the engine as should be readily apparent.
It is, therefore, a principal object of this invention to provide an improved exhaust system for a marine engine.
It is a further object of this invention to provide an exhaust system for a marine engine that embodies an under water exhaust gas discharge and which will insure against the ingestion of water into the engine chambers under any running condition.